1. Field of the Invention
The present application relates to optical metrology, and more particularly to optical metrology model optimization.
2. Related Art
Optical metrology involves directing an incident beam at a structure, measuring the resulting diffracted beam, and analyzing the diffracted beam to determine various characteristics, such as the profile of the structure. In semiconductor manufacturing, optical metrology is typically used for quality assurance. For example, after fabricating a periodic grating in proximity to a semiconductor chip on a semiconductor wafer, an optical metrology system is used to determine the profile of the periodic grating. By determining the profile of the periodic grating, the quality of the fabrication process utilized to form the periodic grating, and by extension the semiconductor chip proximate the periodic grating, can be evaluated.
Determination of the profile model parameters is typically done by selecting the profile model that meets or exceeds matching criteria of profile model optimization using measures such as goodness of fit, cost, and such. Typically, the specific type or types of process control desired for an application is not considered until the end results of the fabrication steps are evaluated. Types of process control typically include wafer-to-wafer control, lot-to-lot control, and/or within-wafer control. Within-wafer control may be die-to-die or site-to-site control within a wafer.